Switches having mechanically separable contact elements and a tripping unit are known as circuit breakers, for example. The tripping unit checks in each case whether the electrical energy flowing via the contact elements satisfies a predefined condition and trips the separation of the contact elements if the condition has been satisfied. An analog signal conditioning device is used to determine the electrical energy flow, which signal conditioning device comprises at least one sensor unit whose sensor directly or indirectly respectively emits an electrical analog signal proportional to the energy. The signal conditioning device also then usually has a normalizing stage for adaptation to different nominal currents. The normalized analog signal is then at least amplified by a downstream amplifier in order to increase the dynamic range of the downstream analog/digital converter, to the input of which the amplified analog signal is passed in addition to the analog signal which has not been amplified. The processor unit in the tripping unit respectively selects which of the two digitized analog signals (digital values) is used to check the predefined condition. In this case, the amplified analog signal is respectively not taken into account if it overloads the analog/digital converter.
If hardware defects occur in the analog signal conditioning device of the electronic tripping unit, these defects may result in the tripping unit no longer correctly responding in the event of a fault and not detecting a short circuit, for example.
When using amplifiers in the signal conditioning device, it is important to also detect their defects in order to avoid false tripping or absent tripping.